RESTRUCTURING EXPENSES - Components of Restructuring Expenses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Balance accrued at December 31, 2018	$ 0	$ 0
Restructuring expenses	7,400	7,420	$ 0	$ 0
Payments		(6,623)
Balance accrued at December 31, 2019		797	0
Workforce reduction
Restructuring Reserve [Roll Forward]
Balance accrued at December 31, 2018	0	0
Restructuring expenses		7,034
Payments		(6,237)
Balance accrued at December 31, 2019		797	0
Contract termination
Restructuring Reserve [Roll Forward]
Balance accrued at December 31, 2018	0	0
Restructuring expenses		229
Payments		(229)
Balance accrued at December 31, 2019		0	0
Other
Restructuring Reserve [Roll Forward]
Balance accrued at December 31, 2018	$ 0	0
Restructuring expenses		157
Payments		(157)
Balance accrued at December 31, 2019		$ 0	$ 0